Writing instrument



FIG. 1 is a perspective view of a writing instrument showing my new ornamental design;

FIG. 2 is a right side elevational view thereof; a left side elevational view is a mirror image of the right side elevational view;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a front end elevational view thereof; a rear end elevational view is a mirror image of the front end elevational view. 

The ornamental design for a writing instrument, as shown and described. 